<?php
/**
 * CodeIgniter
 *
 * An open source application development framework for PHP
 *
 * This content is released under the MIT License (MIT)
 *
 * Copyright (c) 2014 - 2015, British Columbia Institute of Technology
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * @package    CodeIgniter
 * @author    EllisLab Dev Team
 * @copyright    Copyright (c) 2008 - 2014, EllisLab, Inc. (http://ellislab.com/)
 * @copyright    Copyright (c) 2014 - 2015, British Columbia Institute of Technology (http://bcit.ca/)
 * @license    http://opensource.org/licenses/MIT    MIT License
 * @link    http://codeigniter.com
 * @since    Version 3.0.0
 * @filesource
 */
defined('BASEPATH') OR exit('No direct script access allowed');

/**
 * CodeIgniter Session Memcached Driver
 *
 * @package    CodeIgniter
 * @subpackage    Libraries
 * @category    Sessions
 * @author    Andrey Andreev
 * @link    http://codeigniter.com/user_guide/libraries/sessions.html
 */
class CI_Session_memcached_driver extends CI_Session_driver implements SessionHandlerInterface {

    /**
     * Memcached instance
     *
     * @var    Memcached
     */
    protected $_memcached;

    /**
     * Key prefix
     *
     * @var    string
     */
    protected $_key_prefix = 'ci_session:';

    /**
     * Lock key
     *
     * @var    string
     */
    protected $_lock_key;

    // ------------------------------------------------------------------------

    /**
     * Class constructor
     *
     * @param    array    $params    Configuration parameters
     * @return    void
     */
    public function __construct(&$params)
    {
        parent::__construct($params);

        if (empty($this->_config['save_path']))
        {
            log_message('error', 'Session: No Memcached save path configured.');
        }

        if ($this->_config['match_ip'] === TRUE)
        {
            $this->_key_prefix .= $_SERVER['REMOTE_ADDR'].':';
        }
    }

    // ------------------------------------------------------------------------

    /**
     * Open
     *
     * Sanitizes save_path and initializes connections.
     *
     * @param    string    $save_path    Server path(s)
     * @param    string    $name        Session cookie name, unused
     * @return    bool
     */
    public function open($save_path, $name)
    {
        $this->_memcached = new Memcached();
        $this->_memcached->setOption(Memcached::OPT_BINARY_PROTOCOL, TRUE); // required for touch() usage
        $server_list = array();
        foreach ($this->_memcached->getServerList() as $server)
        {
            $server_list[] = $server['host'].':'.$server['port'];
        }

        if ( ! preg_match_all('#,?([^,:]+)\:(\d{1,5})(?:\:(\d+))?#', $this->_config['save_path'], $matches, PREG_SET_ORDER))
        {
            $this->_memcached = NULL;
            log_message('error', 'Session: Invalid Memcached save path format: '.$this->_config['save_path']);
            return FALSE;
        }

        foreach ($matches as $match)
        {
            // If Memcached already has this server (or if the port is invalid), skip it
            if (in_array($match[1].':'.$match[2], $server_list, TRUE))
            {
                log_message('debug', 'Session: Memcached server pool already has '.$match[1].':'.$match[2]);
                continue;
            }

            if ( ! $this->_memcached->addServer($match[1], $match[2], isset($match[3]) ? $match[3] : 0))
            {
                log_message('error', 'Could not add '.$match[1].':'.$match[2].' to Memcached server pool.');
            }
            else
            {
                $server_list[] = $match[1].':'.$match[2];
            }
        }

        if (empty($server_list))
        {
            log_message('error', 'Session: Memcached server pool is empty.');
            return FALSE;
        }

        return TRUE;
    }

    // ------------------------------------------------------------------------

    /**
     * Read
     *
     * Reads session data and acquires a lock
     *
     * @param    string    $session_id    Session ID
     * @return    string    Serialized session data
     */
    public function read($session_id)
    {
        if (isset($this->_memcached) && $this->_get_lock($session_id))
        {
            // Needed by write() to detect session_regenerate_id() calls
            $this->_session_id = $session_id;

            $session_data = (string) $this->_memcached->get($this->_key_prefix.$session_id);
            $this->_fingerprint = md5($session_data);
            return $session_data;
        }

        return FALSE;
    }

    // ------------------------------------------------------------------------

    /**
     * Write
     *
     * Writes (create / update) session data
     *
     * @param    string    $session_id    Session ID
     * @param    string    $session_data    Serialized session data
     * @return    bool
     */
    public function write($session_id, $session_data)
    {
        if ( ! isset($this->_memcached))
        {
            return FALSE;
        }
        // Was the ID regenerated?
        elseif ($session_id !== $this->_session_id)
        {
            if ( ! $this->_release_lock() OR ! $this->_get_lock($session_id))
            {
                return FALSE;
            }

            $this->_fingerprint = md5('');
            $this->_session_id = $session_id;
        }

        if (isset($this->_lock_key))
        {
            $this->_memcached->replace($this->_lock_key, time(), 300);
            if ($this->_fingerprint !== ($fingerprint = md5($session_data)))
            {
                if ($this->_memcached->set($this->_key_prefix.$session_id, $session_data, $this->_config['expiration']))
                {
                    $this->_fingerprint = $fingerprint;
                    return TRUE;
                }

                return FALSE;
            }

            return $this->_memcached->touch($this->_key_prefix.$session_id, $this->_config['expiration']);
        }

        return FALSE;
    }

    // ------------------------------------------------------------------------

    /**
     * Close
     *
     * Releases locks and closes connection.
     *
     * @return    bool
     */
    public function close()
    {
        if (isset($this->_memcached))
        {
            isset($this->_lock_key) && $this->_memcached->delete($this->_lock_key);
            if ( ! $this->_memcached->quit())
            {
                return FALSE;
            }

            $this->_memcached = NULL;
            return TRUE;
        }

        return FALSE;
    }

    // ------------------------------------------------------------------------

    /**
     * Destroy
     *
     * Destroys the current session.
     *
     * @param    string    $session_id    Session ID
     * @return    bool
     */
    public function destroy($session_id)
    {
        if (isset($this->_memcached, $this->_lock_key))
        {
            $this->_memcached->delete($this->_key_prefix.$session_id);
            return $this->_cookie_destroy();
        }

        return FALSE;
    }

    // ------------------------------------------------------------------------

    /**
     * Garbage Collector
     *
     * Deletes expired sessions
     *
     * @param    int     $maxlifetime    Maximum lifetime of sessions
     * @return    bool
     */
    public function gc($maxlifetime)
    {
        // Not necessary, Memcached takes care of that.
        return TRUE;
    }

    // ------------------------------------------------------------------------

    /**
     * Get lock
     *
     * Acquires an (emulated) lock.
     *
     * @param    string    $session_id    Session ID
     * @return    bool
     */
    protected function _get_lock($session_id)
    {
        if (isset($this->_lock_key))
        {
            return $this->_memcached->replace($this->_lock_key, time(), 300);
        }

        // 30 attempts to obtain a lock, in case another request already has it
        $lock_key = $this->_key_prefix.$session_id.':lock';
        $attempt = 0;
        do
        {
            if ($this->_memcached->get($lock_key))
            {
                sleep(1);
                continue;
            }

            if ( ! $this->_memcached->set($lock_key, time(), 300))
            {
                log_message('error', 'Session: Error while trying to obtain lock for '.$this->_key_prefix.$session_id);
                return FALSE;
            }

            $this->_lock_key = $lock_key;
            break;
        }
        while ($attempt++ < 30);

        if ($attempt === 30)
        {
            log_message('error', 'Session: Unable to obtain lock for '.$this->_key_prefix.$session_id.' after 30 attempts, aborting.');
            return FALSE;
        }

        $this->_lock = TRUE;
        return TRUE;
    }

    // ------------------------------------------------------------------------

    /**
     * Release lock
     *
     * Releases a previously acquired lock
     *
     * @return    bool
     */
    protected function _release_lock()
    {
        if (isset($this->_memcached, $this->_lock_key) && $this->_lock)
        {
            if ( ! $this->_memcached->delete($this->_lock_key) && $this->_memcached->getResultCode() !== Memcached::RES_NOTFOUND)
            {
                log_message('error', 'Session: Error while trying to free lock for '.$this->_lock_key);
                return FALSE;
            }

            $this->_lock_key = NULL;
            $this->_lock = FALSE;
        }

        return TRUE;
    }

}
